1. Field of the Invention
The present invention relates to a transfer apparatus that displays an image, which was digitally recorded by a digital still camera (DSC), a video camera, a personal computer (PC), or the like, on a transmission type image display device formed by a liquid crystal display device (hereinafter referred to as “LCD”) or the like, and transfers the image displayed on the transmission type image display device onto (forms the image on) a photosensitive recording medium such as an instant photographic film that develops colors when illuminated by light.
2. Description of the Related Art
As a method for transferring, printing or recording a digitally recorded image onto or on a recording medium, various systems have conventionally been known, examples of which include an ink jet system using a dot-shaped print head, a laser recording system, and a thermal recording system.
A printing system like the ink jet system has various problems. For instance, a long time is taken to perform printing, ink is likely to cause clogging, and precise printing results in a situation where a printed sheet is moistened by ink. Also, the laser recording system requires an expensive optical component such as a lens, which results in a problem that the apparatus cost is increased. Further, the laser recording system and the thermal recording system require considerable power consumption, thereby being not suited for carrying the system, which is also a problem.
Thus, generally speaking, transfer apparatuses using those systems, in particular, transfer apparatuses using the ink jet system have such a problem that the more precise printing is performed in the apparatus, the more complicated the driving mechanism and the control mechanism become, as well as the larger and the more expensive the apparatus become. In addition, there is a problem in that a long time is taken to perform printing.
In this regard, a transfer apparatus is proposed in which a display image is formed on a photosensitive recording medium such as an instant film using an LCD, thereby achieving simplification of an apparatus structure and a reduction in cost (see JP 10-309829 A and JP 11-242298 A, for instance).
The electronic printer (transfer apparatus) disclosed in JP 10-309829 A is capable of copying the display screen of a liquid crystal display onto a photosensitive medium to thereby produce a hard copy having a photographic quality. On the other hand, in the case of the printing apparatus disclosed in JP 11-242298 A, there is no need to use an expensive optical component such as a lens, and to secure an appropriate focal length. Thus, as compared with the conventional transfer apparatuses, a further reduction can be achieved in terms of size, weight, power consumption, and cost.
FIG. 22A is a side view of the printing apparatus disclosed in JP 11-242298 A and FIG. 22B is an enlarged view of a portion D of FIG. 22A. In this printing apparatus, as shown in FIG. 22A, a photosensitive film 400 is brought into intimate contact with the display surface of a transmission type LCD 300, and a light source (backlight 100) provided on the opposite side of the LCD 300 with respect to the photosensitive film 400 is turned on. That is, a fluorescent lamp 101 is switched on to turn on the backlight 100. In this manner, an image displayed on the LCD 300 is printed onto the photosensitive film 400. Here, as shown in FIG. 22B, the LCD 300 includes a polarizing plate 301 and a glass substrate 302 on the display surface side, a liquid crystal layer 303, and a glass substrate 304 and a polarizing plate 305 on the backlight 100 side. Also, the total thickness from the polarizing plate 301 to the polarizing plate 305 is set at 2.8 mm.
FIG. 23 is a perspective view of a printing apparatus according to another embodiment disclosed in JP 11-242298 A. In the embodiment disclosed in JP 11-242298 A, as shown in FIG. 23, a lattice 200 is provided between the backlight 100 and the LCD 300, thereby suppressing diffusion of light from the backlight 100. That is, the lattice 200 approximates the light from the backlight 100 to parallel rays. Further, a spacer 201 formed by a rectangular hollow case is provided between the lattice 200 and the LCD 300, thereby preventing an image of a frame of the lattice 200 (shadow due to the frame) from being taken by the photosensitive film 400. With this construction, clarity of an image formed on the photosensitive film 400 is improved to a satisfactory degree from the practical point of view without providing an optical component and securing an appropriate focal length.
Also, JP 11-242298 A discloses an example of a printing apparatus in which the total thickness of the LCD 300 is set at 2.8 mm, as shown in FIG. 22B, and a screen of the LCD 300 displayed with a dot size of 0.5 mm is printed onto the photosensitive film 400. In this printing apparatus, a lattice 200 that has a thickness of 10 mm and is provided with 5 mm2 through-holes is provided in order to prevent diffusion of light emitted from the LCD 300, and a 20 mm spacer 201 is arranged between the lattice 200 and the LCD 300. Further, the LCD 300 and the photosensitive film 400 are brought into intimate contact with each other to effect printing without causing blurring (unclarity) of the image.
In addition, as a transfer apparatus that realizes reductions in size, weight, power consumption, and cost with a simplified construction and is suited for carrying the apparatus, a transfer apparatus is, for instance, known in which a light source, a light linearizing unit, a transmission type image display unit, and a photosensitive recording medium are arranged along an advancing direction of light from the light source, the light from the light source is converted by the light linearizing unit into linear and substantially parallel rays and is caused to perpendicularly enter a display surface of the image display unit, and the image display unit is relatively scanned by the linear and substantially parallel rays, thereby transferring a display image having passed through the image display unit onto the photosensitive recording medium (see JP 2002-196424 A, JP 2002-196425 A, JP 2002-196426 A, and the like, for instance).
However, in the transfer apparatus disclosed in JP 10-309829 A, in order to copy the display screen of the liquid crystal display onto the photosensitive medium, an optical component such as a rod lens array, needs to be arranged between the display screen of the liquid crystal display and the photosensitive medium, which leads to a problem in that the apparatus cost is increased by the expensive optical component. Also, a predetermined distance (total conjugate length) needs to be set between the liquid crystal display and the photosensitive medium, which imposes a limitation on a reduction in the apparatus size. In JP 10-309829 A, for instance, it is necessary to secure a total conjugate length of 15.1 mm.
Further, in the printing apparatus disclosed in JP 11-242298 A, an image is obtained by bringing the LCD and the photosensitive film into intimate contact with each other and printing the image onto the photosensitive film. In this case, several colors are mixed with each other and therefore it is difficult to precisely reproduce the colors, which results in a problem in that the quality of an image transferred onto the photosensitive film is degraded. Reasons for this will be described below.
That is, first, in order to present an image that is to be felt beautiful and bright by a human, a red (hereinafter referred to as “R”) color filter, a green (hereinafter referred to as “G”) color filter, and a blue (hereinafter referred to as “B”) color filter provided for a color LCD are each generally produced to have high transmittance and a wide transmission wavelength range.
FIG. 5 is a graph in which the spectral transmittance curves of the RGB color filters are plotted with transmittance as ordinate against wavelengths as abscissa. In FIG. 5, there are shown examples of the spectral transmittance curves R1, G1, and B1 of the color filters of the LCD. As shown in FIG. 5, each color filter of the LCD is produced so as to have a wide transmission wavelength range. Accordingly, in the vicinity of a wavelength of 600 nm, the transmission ranges of R light and G light overlap each other. Also, in the vicinity of a wavelength of 500 nm, the transmission ranges of B light and G light overlap each other. In each of such overlapping ranges, light in one color and light in another color are both allowed to pass through the color filters.
Further, when a cold-cathode tube is used as the backlight light source of the LCD, the light-emission range of a fluorescent material used in the cold-cathode tube is increased as much as possible in order to increase a light quantity. Further, in order to realize an image that is to be felt bright by a human, the intensity of G light is generally increased.
FIG. 24 is a graph in which the spectrum waveform of the backlight light source of the LCD is plotted with light intensity as ordinate against waveforms as abscissa. The spectrum waveform of the light source shown in FIG. 24 is a spectrum waveform of a cold-cathode tube of a so-called three-wavelength type. As shown in FIG. 24, the spectrum waveform has the biggest peak in the vicinity of a wavelength of 550 nm at which G light is emitted, and also has big peaks in the vicinity of a wavelength of 580 nm and in the vicinity of a wavelength of 490 nm.
Further, the photosensitive film onto which an image is to be transferred, has a considerable peak in each wavelength range in which color development is performed with one of R light, G light, and B light. However, the color development range of the R light and the color development range of the G light overlap each other at their boundary, and the color development range of the G light and the color development range of the B light overlap each other at their boundary.
FIG. 25 shows the spectral sensitivity distribution of an instant film for use in “cheki” (manufactured by Fuji Photo Film Co., Ltd.) that is an example of the photosensitive film. In FIG. 25, the spectral sensitivity characteristics of the photosensitive film with respect to the R light, the G light, and the B light are plotted with sensitivity as ordinate against wavelengths as abscissa. As shown in FIG. 25, even in the case of this instant film, overlapping of the color development ranges of the R light and the G light occurs in their boundary range of 570 to 600 nm and overlapping of the color development ranges of the G light and the B light occurs in their boundary range of 480 to 510 nm, although their overlapping degrees are small.
Accordingly, at the boundary range (color mixture range) at which color developing is performed with both of the R light and the G light, light having the wavelength in this range (light whose peak exists in the vicinity of 580 nm and in the vicinity of 480 nm) develops both of R and G colors on the photosensitive film. Also, at the boundary range (color mixture range) at which color development is performed with both of the G light and the B light, both of G and B colors are developed. As a result, color mixture occurs in a resultant image and therefore the image quality is degraded.
In the above description, a case where the light source emits each of the R light, the G light, and the B light has been explained. Even when one of RGB colors is displayed on the LCD and the photosensitive film is exposed with the single color, mixture with another color also occurs. This will be described below by taking a case of G color as an example.
In order to display only the G color on the LCD, setting is made beforehand so that light is allowed to pass through only dots of the G color filter of the LCD and is not allowed to pass through dots of the R and B color filters. Under this condition where only the G color is displayed on the LCD, the three-wavelength-type cold-cathode tube shown in FIG. 24 is turned on for a required time. Note that at this time, the three-wavelength-type cold-cathode tube emits light at all wavelengths at which it is capable of performing light emission. This light is allowed to pass through the G color filter of the LCD and reach the photosensitive film. Accordingly, the light that can reach the photosensitive film becomes light obtained by multiplying the light wavelength of the G color filter of the LCD by the transmittance of the G color filter.
FIG. 26 is a graph in which the spectral intensity characteristics of light having passed through the G color filter of the LCD are plotted with light intensity as ordinate against wavelengths as abscissa. In the intensity distribution of the light having passed through the G color filter shown in FIG. 26, transmission light exists in a gently inclined B range of around 440 to 480 nm and has a small peak in the vicinity of 490 nm. Also, in an R direction (on a long wavelength side), transmission light having a peak exists in the vicinity of 580 nm and transmission light having a small peak exists in the vicinity of 610 nm. Among those, in particular, transmission light at 490 nm contains light in the B range of the film.
That is, even if a light source having the spectral wavelength characteristics shown in FIG. 24 is used to display G color on the LCD and expose the photosensitive film, reproduced G color is mixed with B color to some extent, although the color of an image transferred onto the photosensitive film has a color that is almost the same as the original G color.
FIG. 28 shows a result of exposure of the photosensitive film in the manner described above. In FIG. 28, results of color development of RGB colors are plotted with densities as ordinate against gradation as abscissa. In FIG. 28, in a downward direction on the ordinate, the density is reduced (that is, brightness is increased) and therefore the degree of color development is increased. As shown in FIG. 28, in addition to the graph of G color, the graph of B color also moves in the downward direction and the B color is also developed to some extent. For instance, at the gradation of 120, the density of G is around 1.0 and the density of B is 1.74. As a result, it is found that B is slightly mixed into G.
Also, usually, the spectral sensitivity characteristics of the photosensitive recording medium like the instant film described above are adjusted so as to be suited to daylight or electronic flash light, which means that the spectral sensitivity characteristics of the photosensitive recording medium are not suited to the light source spectrum of the cold-cathode tube that is the light source of the liquid crystal display. Therefore, there arises a problem in that the gray tone is not correctly reproduced. Also, when gray is displayed on the liquid crystal display, the mismatching degree with the spectral sensitivity characteristics of the photosensitive recording medium is increased due to the characteristics of the color filter applied to the liquid crystal display and therefore an image formed on the photosensitive recording medium takes on a blue tinge, for instance.
Further, basically, when the RGB components of the light from the light source are equally mixed with each other, gray (between black and white) is obtained. However, the spectral sensitivity characteristics of the photosensitive recording medium do not match the light source spectrum as described above, so that it is necessary to control light passing through the liquid crystal display by, for instance, adjusting the light source with reference to the difference in terms of the spectral sensitivity characteristics of the photosensitive recording medium.
As described above, in the conventional transfer apparatuses, color mixture inevitably occurs, so that there arises a problem in that it is impossible to obtain an image having an appropriate color and the image quality is degraded. In view of this problem, it is desired not only to simply transfer an image displayed on an LCD but also to obtain a high quality image by improving color reproductivity.